TIRES: One for all?

Tire choices are dictated by operating goals

In a perfect world, fleets would equip their tractors with all-position rib tires on the steer axle, as well as the inner and outer duals of the drive axle. The reason is fairly obvious: saving money. First of all, keeping just two types of tires in inventory — one model for steer and drive axles and another for trailers — is less expensive than keeping a variety of tires in stock. This is true whether a fleet is stocking its own inventory or a supplier is doing it for them.

In the second place, using rib tires can mean saving money on fuel. A good rib tire, which has less tread than a thicker drive tire, is going to produce less rolling resistance, translating into better fuel economy.

“That lower rolling resistance gives you tremendous fuel savings — a 3% to 5% improvement in fuel economy,” says Ron Gilbert, national director of sales-commercial tires for Toyo Tires. “You would need to rotate them more frequently back to front to help even out tread wear, but from the fuel savings alone you'd still be ahead.”

Finally, using an all-position rib tire all the way around the tractor saves a fleet big time in terms of tire pricing. “It'll save you $1,000 to $2,000 per power unit (about $100 per tire) using ribs all the way around, excluding the trailer axle position,” says Curtis Decker, manager of field engineering at Continental Tire North America (CTNA). “That's a big upfront savings.”

It all totals up to some pretty compelling reasons for a fleet to switch to an all-position tire, doesn't it? But since fleets don't operate in anything close to a perfect world, choosing all-position tires may be an option for only a very small segment of trucking companies, at best.

“We prefer to use position-specific treads, because our equipment runs in such a wide variety of applications — in-city pickup and delivery (P&D), regional runs, and long-haul operations across plains and mountains, with all different kinds of weather to contend with,” says Jim Law, national tire manager for truck leasing and maintenance giant Ryder.

“We want tires in P&D fleets to be able to withstand sidewall damage, or have tires with good traction for our customers that frequently operate in severe weather, such as snow, or who need to operate off-road as well as on-highway,” he says. “In our situation, with such a diversity of equipment, applications and operating environment, it makes sense to use position-specific tires.”

Doug Jones, customer engineering support manager at Michelin Americas Truck Tires, says the only time it's a good idea to use just all-position tires is “if a fleet's main concern is fuel economy, because they usually have a lower rolling resistance than drive and trailer tires.” He continues, “However, using specific-position tires…provides better handling and traction because they are optimized for those specific positions, and are also designed for better and longer wear.”

Phillip Boartes, marketing director for commercial products at Cooper Tire & Rubber Co., agrees that traction is one of the real pluses to using position-specific tires, along with longer mileage and better life cycle cost. He feels that the biggest benefit, though, is that they're designed to withstand the unique rigors of particular applications, such as off-road use.

“Take a tire that'll run 70% on-road and 30% off-highway, such as in a logging fleet. You'll need a particular tread and rubber compound to handle that — one that can withstand chipping and cutting,” he explains. “Chips and cuts wear out the tire early…you have a better chance of getting more life out of the tire [if you spec] a specific type. In the end, you need the right tire for the right application.”

Axle Power

Another key to tire selection is axle power — or the lack of it. The amount of force applied to the tire varies vastly from one position to another. This, in turn, impacts a tire's life expectancy; if force is excessive, tires degrade faster, thus boosting costs for an unsuspecting fleet.

“Trucks produce a lot more horsepower and torque today than in the past,” says Ken McKibben, senior vp-field maintenance for Penske Truck Leasing. “Today a typical highway tractor is producing 500 hp. and 1,600 lb.-ft. of torque, all of which goes through the drive axle. Because of that, casings do not last as long as they once did.”

Continental's Drecker emphasizes the role of a fleet's operating style. “If you've got 460-hp. engines governed at 62 mph, there's an advantage to rib tires in the drive position. But if you've got 500-hp. engines and are running 65 to 75 mph — no matter what the load — with no downshifting at the hills, that's a whole different story,” he points out. “That rib tire…will melt in the drive position under that amount of force.”

Although steer tires feel the effects of some of that engine power, it's all of the turning and twisting from maneuvering on and off highways or through city streets that really creates stress on their treads and casings.

Guy Walenga, engineering manager for Bridgestone/Firestone North America Tire, explains the impact of P&D operations on steer tires. “[They] are brutally used. They need deeper tread because it gets knocked off fast, and they need a high strong sidewall to preserve the tire against impact with curbs and such,” he says. “In this case, you don't want a 16/32nd standard steer rib; you definitely need deeper tread.”

Back at the trailer position, however, tire experts recommend fleets use nothing but shallow retread tires — with tread depth between 11/32nd and 13/32nd.

“We found out long ago that less is more when it comes to trailer tires,” says Tim Miller, marketing and communications manager for Goodyear Tire & Rubber Co. “Because trailer axles are ‘free rolling,’ with no driving force running thru the axle, they can get higher miles with shallower tread. Without axle force, a deeper tread won't be able to clean itself of snow or slush and it will be more vulnerable to irregular wear. That's why a good shallow retread tire is going to be more likely to survive back there [on the trailer axle].”

Another advantage to position-specific tires is tread depth. If a fleet chooses all-position tires, it's also choosing to go with equal tread depth in all positions, something that might actually be more costly over the expected life of a tire.

“If you go with an all-position tire, you are usually looking at uniform tread depth of 18/32nd; that's a lot of rubber for the steer axle and invites irregular wear,” says Bridgestone/Firestone's Walenga. “On the drive tire, you may get a little better fuel economy with an all-position tire, but you'd have to give up an awful lot of tread depth, as typical drive is around 30/32nd. Not only do you lose traction with an all-position tire, you'll take that tire out of service long before a deeper tread position-specific tire, and you lose money there.”

“A good, new drive tire is going to give you 250,000 miles of life before you need to pull it for retreading, but a good rib tire only 130,000 miles,” adds Continental's Decker. “So you're giving up a full year of tire life if you choose to run ribs all the way around.”

Walenga notes another key benefit to deep-tread drive tires “It stays in the sweet spot of best fuel economy tread depth longer since it has more tread to wear off,” he says. “Overall, it gets to the point where fuel economy stays the same between all-position and position-specific tires on the drive axle simply because you have to pull the all-position tire sooner; it doesn't have as much tread to wear off.”

And the reason all-position tires don't have the extra tread is that they're a compromise design from the start, adds John Cooney, director of commercial sales for Yokohama Tire.

“All-position tires are not the deepest nor the shallowest when it comes to tread depth,” he notes. “They are designed without all the special features of position-specific tires because by choosing them you are not expecting to encounter all of the hazards common to long-haul trucking: severe weather, road debris, gravel shoulders, etc. That's why the more miles a fleet operates cross-country, the more it will need to use axle-specific tires.”

Perfect world or not, the best tire for your fleet is not just a matter of application and operating environment. It's also a matter of what's most important to you, i.e., which goal would you like your tires to help you achieve?

“Before even starting to tire type, fleets must pick one specific target to shoot for,” says Continental's Decker. “What's your top priority? Fuel economy? Or on-time arrival and performance? Fleets get into trouble when they try to get their tires to do everything at once, [such as] provide exceptional traction, fuel economy, and life cycle cost.”

Decker emphasizes that while you shouldn't ignore the other factors, you need to decide which is most important to your fleet. This will enable you to select the tire or tires that will best meet your goals.

For example, if fuel economy is your primary concern, Decker points out that there's a distinct advantage to putting rib tires all the way around a tractor since they have less tread depth and thus have fuel efficiency built in. “That makes fuel economy king and traction second. This would work for a regional fleet in the Southwest, with flexible scheduling that's not just-in-time (JIT) driven, and maybe experiences severe rains every now and again.”

However, if on-time arrival is a fleet's top concern, then it needs to be able to function in all types of weather conditions. “You need traction now; that's your number-one priority,” says Decker. “So you need to focus on spec'ing tires specific to each axle, deep-tread drive tires and solid ribs for the steer axle.”

Decker thinks that fleets are best served if they make tire-spec'ing decisions based on operating style and cost model. “You must cost-justify the tire you're choosing based on what you are trying to do,” he says. “That cost-justification should take all of your variables into account as well: Do you need to be on time, have a bulletproof tire package, etc.”

For those reasons, Goodyear's Miller believes position-specific tires make the most sense. “The right tire for the right axle is still the right policy,” he says.

Tire Care Maxims

Whether you choose all-position or position-specific tires for your fleet, Pat Keating, senior tire engineer for Hankook Tire America Corp., has some pointers to help you get the most out of your investment.

Maintain proper tire pressure

“That's the most important thing you can do to make sure you get the most life and use out of your tires,” he says. Poorly under-inflated or over-inflated tires, especially for steer axles and trailer tires, could cost you 20% of a tire's life expectancy.

Curb Aggressive Driving

Driving over 60 mph, making sharp turns, and braking hard take a big toll of tires, warns Keating. “Lateral forces going through the tire at high speed during maneuvers and hard braking increase exponentially, cutting tire life by between 20% and 30%,” he says. “Fast starts and stops also drive a lot more torque through the tire, so the less force you apply through that small contact area between the rubber and the road, the more life you'll get from your tires.”

Tire rotation and alignment count

Following a rotation and alignment schedule can save money over time. “They fight heel/toe wear on the tire and help even out tread wear over the tire's life,” Keating notes. Improper tire alignment can cost you 5,000 to 10,000 miles of a tire's life.

Focus on cost per mile

To make sure you're maximizing tire life, track them via a cost-per-mile system.

Life Expectancy

With so many different variables affecting tire mileage, from proper inflation to driving habits, tire makers can't guarantee precisely how long a given tire will last. However, Hankook's Pat Keating says the following can serve as a general guideline. Assuming, of course, that fleets take good care of their rubber.

Steer tire: 100,000 to 150,000 miles; tread thickness — 18/32 to 21/32nd.

Drive tire: 250,000 to 300,000; tread — 28/32 to 30/32nd.

Trailer tire: 90,000 to 100,000 miles; retreads that are 12/32 to 14/32nd thick. Keating says fleets should opt for retreads for this position, rather than buying new tires.

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